I only do over 6 hours for boardgames. I've several great ones that have expected playtimes of 6-18 hours. (Advanced Civilization, Pax Britannica, Federation Space.) Tho' for a couple decades, a 6 hour sunday session was standard: 2pm to 8 pm.
I used to have Supremacy, and that is another 6-18 hour. My last play was with all the options added, 18 hours, 4 star victory.
And the 3-8 hour choices of Samurai Swords (aka Shogun), Axis and Allies, SFB (for a BATS or SB assault scenario)...
3-6 hours for 1856.
Fortune and Glory is 2.5-8 hours, depending upon mode and whether teaching it or everyone knows it, and the long tail is to the right.
A full game of Mah Jongg with 4 players can be 3-8 hours (that's 16 hands), depending upon playstyles and luck.